Edit report at https://bugs.php.net/bug.php?id=76827&edit=1
ID: 76827
Comment by: zjz at zjz dot name
Reported by: zjz at zjz dot name
Summary: Introduce a new function struncate or some such
Status: Open
Type: Feature/Change Request
Package: Performance problem
PHP Version: Irrelevant
Block user comment: N
Private report: N
New Comment:
Well. Let me try to look into the C code and then gives some code example to explain what I said.
Previous Comments:
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[2018-08-31 09:56:40] zjz at zjz dot name
$str = substr($str, 0 , -1); first makes a new string by the truncated length, and then frees the
original string, which seems to me uncessary.
As to why I suggest this new function with a reference parameter, **I didn't AT ALL try to mean
that referencing itself is more effient**, but I just meant in the new function, **something magic**
can be done in C code in the new function, so that the original string can be **directly**
truncated, without making a new truncated string in another place at first, and then freeing the
original one, which is uncessary.
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[2018-08-31 09:08:10] spam2 at rhsoft dot net
you miss the point:
a new function with a reference would gain *nothing* which couldn't be done in substr() too
without clutter the function list
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[2018-08-31 09:04:39] zjz at zjz dot name
I think I understand the copy-on-write nature, I am just not sure it can avoid copying **if the
substr can optimise out** the copying when the variable that receives the returned value is as the
same one as the passed parameter.
I haven't right now looked into the C code, but from what I guess, substr doesn't know
before hand if the variable that receives the returned value is as the same one as the passed
parameter, so the process I guess is like the following:
Step 1. Copying the string by the truncated length. (in the process of calling substr)
Step 2. Do the assignment(in the process of $str = substr()), now the original string is
dereferenced and its reference count is zero, so it's freed in this step.
So I want to repeat what I said in my previous comment: is PHP smart in that if the variable that
receives the returned value is as the same as the one passed as the parameter, it can avoid copying?
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[2018-08-31 08:46:19] spam2 at rhsoft dot net
why the hell should it copy the param and why do you think a reference is helpful?
http://www.phpinternalsbook.com/zvals/memory_management.html
http://schlueters.de/blog/archives/125-Do-not-use-PHP-references.html
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[2018-08-31 08:42:25] zjz at zjz dot name
Thanks for the reply.
So if substr doesn't do copying, then what if I use a different variable(say $str1) to receive
the truncated string from $str.
$str1 = substr($str, 0, -1);
Doesn't it do copying?
Or did you mean that PHP is smart in that if the variable that receives the returned value is as the
same as the one passed as the parameter, it can avoid copying?
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